Method of coating rigid cores and product thereof

ABSTRACT

Industrial rollers are prepared by photocuring a layer of photocurable composition on the rigid core and then photocuring a layer of diluted photocurable composition to obtain a smooth uniform glazelike finish. As the core cylinder is rotated, a thin layer of photocurable composition is fed intermittently or continuously onto the rotating cylinder, where it can optionally be smoothed by a doctor blade. The photocurable composition preferably is photocured by an ultraviolet light source which is located on the cylinder side opposite the place where the photocurable composition is applied so that premature hardening does not occur in the feed stock. Multiple, consecutive layers of photocurable composition can be built up on the rigid core, each (after the first) being placed upon a partially hardened photocured sublayer. In this manner, the photocured material on the rigid core can be built up to any desired and practical thickness. A solvent-diluted photocurable composition is then coated on the coated core and photocured to furnish the smooth glazelike finish. Toluene is the preferred solvent.

D United States Patent [151 3,637,41 9 Lundsager [4 1 Jan. 25, 1972 [54]METHOD OF COATING RIGID CORES Primary Examiner-Alfred L. Leavitt ANDPRODUCT THEREOF Assistant Examiner-J. H Newsome Attorney-Kenneth E.Prince [72] Inventor: Christian B. Lundsager, Ashton, Md. [73] Assignee:W. R. Grace & Co., New York, NY. [57] ABSTRACT Industrial rollers areprepared by photocuring a layer of [22] Flled' 1969 photocurablecomposition on the rigid core and then [2]] Appl. No.: 879,503photocuring a layer of diluted photocurable composition to obtain asmooth uniform glazelike finish. As the core cylinder is rotated, a thinlayer of photocurable composition is fed in- [52] U.S. Cl. ..ll7/93.31,117/132 R, 117/161 R, termmemly or continuously onto the rotatingcylinder, where 1 17/161 1 6 3 204/l59'l5 it can optionally be smoothedby a doctor blade. The Int Cl 2 4/ 26 photocurable compositionpreferably is photocured by an ul- "aviolet light Source which islocated on the cylinder side [58] Field of Search 17/93'31 1 l6] 161posite the place where the photocurable composition is ap- 4 g i ii 3 2plied so that premature hardening does not occur in the feed I 0 M 6 656 stock. Multiple, consecutive layers of photocurable composi- 26 I7 88 5 R tion can be built up on the rigid core, each (after the first)being placed upon a partially hardened photocured sublayer. [56]References cued In this manner, the photocured material on the rigidcore can UNITED STATES PATENTS be built up to any desired and practicalthickness. A solventdiluted photocurable composition is then coated onthe 1,182,982 5/1916 Crump ..118/409. coated core and photocured tofurnish the smooth glazelike 2,270,177 1/1942 Vawryk. ..118/409 finish.Toluene is the preferred solvent. 3,369,922 2/1968 Svrchek. 117/94 X3,506,626 4/1970 Warner... ..260/79 18 Claims, 3 Drawing Figures3,535,193 10/1970 Prince ..117/93.31 X

ATENTEU memsrz 3637.419

ll/I/l/ FIG. I

IIIIII/l mvmma CHRISTIAN B. LUNDSAGER M Wgaw ATTORNEY PATENTEMmzsLm SHEU2 OF '2 I I l INVENTOR CHRISTIAN B. LUNDSAGER ATTORNEY METHOD OF COATINGRIGID CORES AND PRODUCT THEREOF OBJECTS OF THIS INVENTION It is anobject of this invention to prepare and apply coatings to rigid cores,when said coatings have uniform smooth glazelike finishes. Other objectswill be obvious to those skilled in the art.

BROAD DESCRIPTION OF THE INVENTION Industrial rollers can be prepared bythe process described in copending patent application Ser. No. 879,175,inventors: Hubbard, B. W., Jr., and Kehr, C. L., filed Nov. 24, 1969,said process involving placing a layer of a photocurable composition ona revolving rigid core and photocuring the layer. This inventioninvolves placing a glassy, uniform, smooth, defectfree surface on thoserollers.

The basic rollers are made as follows: The cylinder is rotated at arelatively slow rate of speed, i.e., between about 1 rpm. and 50 r.p.m.,or just below the speed at which centrifugal force, which depends on thediameter of the roller, begins to distort the coating before it isphotocured. A thin layer of photocurable composition is fed onto therotating cylinder, where it can optionally be smoothed by a doctorblade. Also, optionally, a pressure roller can be used to work thecoating and squeeze out air pockets or other gas bubbles. Liquids ofvarious viscosity ranges or thixotropic pastes are preferred but withsuitable modifications of the feeding mechanism, semisolid or solidresinous or elastomeric photocurable compositions can also be handled;the main point is to select a photocurable composition which in thephotocured state will have the desired physical properties and solventresistance for the intended application that the roller will be usedfor. During the application of the photocurable composition to therotating core, the photocurable composition is intermittently orpreferably continuously photocured by an ultraviolet light source.Preferably, the U.V. light source is located on the cylinder sideopposite the place where the photocurable composition is applied so thatpremature hardening does not occur in the feed stock which is maintainedin the shadow cast by the core relative to the U.V. light source.Multiple consecutive layers of the same or different photocurablecompositions can be placed on the rigid core, each (after the first)being located upon a partially or completely hardened photocuredsublayer. In this manner the photocured material on the rigid core canbe built up to any desired and practical thickness, say, for example, 2inches or more. Each layer, as it is applied, will normally be betweenabout 0.5 and about 125 mils in thickness although this is not criticaland may vary greatly depending on the speed of rotation of the core, theviscosity of the photocurable composition, and the curing rate of thephotosensitive material. The photocured surface on the roller, can ifdesired, be ground and buffed to help make an end product having anextremely smooth surface and an accurate cylindrical shape.

This invention involves similarly coating a solvent-diluted photocurablecomposition on the already partially photocured layer to produce aglossy, uniform, smooth finish. The process involves photocuring thesolvent-diluted photocurable composition layer. The heat in the coatedroller from the photocuring of the previous coating of photocurablecomposition is usually sufficient to cause evaporation of the majorityof the solvent, and the small remaining amount of solvent evaporatesduring the subsequent photocuring and storage of the roller. There havebeen no indications by odor or softness of any harmful quantity ofsolvent in the photocured finish coating. So the process is, by way ofsummation, temporarily removing the photocuring radiation source(usually U.V. light), coating the roller with a layer of photocurablecomposition diluted with suitable solvent, allowing evaporation ofsolvent to leave a glossy layer of uncured photocurable composition, andphotocuring that layer with a photocuring radiation source. Thephotocurable composition in the finishing layer is liquid itself or thesolvent mixture within which it incorporated is liquid.

An advantage of this invention is that expensive molds or long heatingcycles are not needed to coat a rigid core. The process of thisinvention is quick, convenient and economical, and produces a superior,fully cured product, which has an extremely smooth, glazelike surfacewithout the need for grinding and buffing. Postfabrication curing oraging steps are not required, since the application and photocuring tocompletion (e.g., to constant final physical properties) of thephotocurable composition is almost simultaneous.

DETAILED DESCRIPTION OF THE INVENTION The invention may be more clearlyunderstood by reference to the following detailed description which isnonlimiting but which merely exemplifies one of the preferredembodiments:

FIG. 1 is an end view, partially cross-sectional, of the apparatusbefore the coating process commences;

FIG. 2 is the same as FIG. 1 except that the coating process is inprogress; and

FIG. 3 is the same as FIG. 1 except that one embodiment the glossyfinish coating process is starting.

Referring to FIG. 1, roller core 4 rotates in a counterclockwisedirection. The mounting and moving means (not shown) for roller core 4is any conventional device capable of rotating the core about its ownaxis (e.g., it is mounted on a lathe). Roller core 4 (1.0-inch diameterby 10 inches) can be cleaned before coating, and, in cases of metalrollers comprised of steel, can be sandblasted prior to mounting toremove any rust and to expose a clean and slightly roughened coatingsurface. Adhesive bonding agents or primers may be applied if desired toimpart good adhesion of the photocurable composition to the coresurface. Reservoir 8, which may be heated if desired, containsphotocurable composition 12. (After photocurable composition 12 isprepared, it must be stored in a dark area, i.e., in the absence ofultraviolet light.) Delivery tray 16 is in a slightly sloping position,with the lower end (delivery lip) about 2 to 20 mils from the surface ofroller core 4 during operation and start up (as shown in FIG. 2) andwith the upper end (receiving portion) positioned under delivery throat20 of reservoir 8. A plurality of delivery throats, etc., can be used toinsure that there is coverage over the entire roller length.Photocurable composition 12 is gravity fed down delivery tray 16.Delivery tray 16 is moveable in a horizontal manner in relationship toroller core 4. Also delivery tray 16 has sidewalls (not shown) toprevent lateral overflow. U.V. light source 24 (e.g., one or several275-watt Westinghouse RS sunlamps, is located so that its irradiatingface is about 1.5 inches from the surface of roller core 4. Severalsunlamps can be used, or a long tubular lamp could be used if desired.Shield 28 encompasses light source 24, except that slit 32 (0.75 inch by10 inches) allows the ultraviolet light to be beamed directly onto thesurface of roller core 4 without exposing photocurable composition 12 indelivery tray 16. The ultraviolet light can be kept from exposing anyphotocurable composition coated on roller core 4 and coating 36 by meansof moveable shield (shutter) 40 (shown in FIG. 3) or by turning it off.

In operation, roller core 4 is typically rotating at about 10 rpm. Valve44 is opened in such. a manner as to properly control the amount ofphotocurable composition 12 flowing down delivery tray 16. Light source24 is activated. As photocurable composition 12 contacts the surface ofrotating roller core 4, it adheres thereto as a layer (i.e., coating 53as in FIG. 2). It is seen that since the direction of rotation of rollercore 4 is counterclockwise, the lip delivery tray 16 serves as a doctorblade to control the thickness of the applied coating on each pass.During the coating operation, "rolling bank" 48 of viscous photocurablecomposition 12 is preferably maintained in the end of delivery tray 16against the surface of core 4. As the uncured coating passes U.V. lightsource 24, it is photocured. The coating thickness can be increased byapplying another coating of uncured photocurable composition 12 onphotocured'composition 12 by moving the edge of delivery tray 16 slowlyaway from coated roller core 4. Coating thicknesses as great as about2.0 or more inches can be obtained, and customary total thicknesses upto about 0.5 to 1.0 inch are easily obtained. After achieving thedesired coating thickness, delivery tray 16 is retracted away from thecoated surface of roller core 4. The roller can be rotated for severalseconds to several minutes thereafter to insure a complete photocure ofthe coating of photocurable composition 12. The coatings are essentiallynontacky and are usually applied in less than l5 to 30 minutes of totaloperating time, depending on the ultimate coating thickness, theintensity of the light source, etc., U.V. light source 24 is thenprevented from shining on coating 36 by means of shield 40 or by turningit off. In the preferred embodiment, shown in FIG. 3, some ofphotocurable composition 12 is placed at the end of delivery tray 16that has been situated very close (or tightly against if the rotation ofthe roller has been stopped) coating 36. Solvent 52 is placed on top ofthe photocurable composition 12 on delivery tray 16. This combination isapplied on top of coating 36 in a manner similar to the one describedabove for coating roller 4. Light source 24 is allowed to photocure thecoated and diluted photocurable composition. In this and otherembodiments, it is preferred the light source be shut off while thediluted photocurable composition is applied so that prematurephotocuring does not occur. A glossy finish is obtained. The mixingaction of the rotating roller blended composition 12 with solvent 52. Inanother embodiment the last coating is done similarly with premixedcomposition 12 and solvent 52. Also, the dilution of composition 12 canbe progressive in that greater amounts of solvent 52 are constantlyadded to the composition l2solvent 52 material being coated. In stillanother embodiment another reservoir is used which contains bothcomposition 12 and solvent 52, and the coating procedure is similar tothe above coating procedure for composition 12. Glossy finishes areobtained in each embodiment.

The photocurable composition to form the outer glossy finish can bediluted to the proper dilution range with a large number of solvents,but toluene is the preferred solvent. Other suitable solvents includeisopropanol, propanol, methanol, ethanol, benzene, acetone, water,methyl ethyl ketone, cellosolve, butyl cellosolve, hexane, methylenechloride,-etc. The solvent must be readily miscible with or emulsifiedwith the photocurable material, yet have little action on the photocuredportion of the roller. Most of the solvent occurs during the rotation ofthe roller before the photocuring occurs. The photocuring of the glossyfinish accomplishes some of the evaporation, including the photocuringafter the composition application has been finished. The remainingsolvent must readily evaporate after the glossy finish is applied, evenif some external heat must be applied.

The dilution ratio (weight-to-weight basis) of solvent to photocurablecomposition should be at least 0.25:] and preferably should be greaterthan 2:1. The solvent is added to the bank in such a manner that thesolvent content gradually increases to nearly 100 percent as thephotocurable composition is used up.

The photocurable composition, as the main portion of the roller coatingand/or as the outer glossy finish, can be added at elevatedtemperatures.

The core is typically constructed of a metal, e.g., aluminum, copper,steel, etc., but also can be constructed of a nonmetallic substance. Thecore can be a solid cylinder, a porous sin tered cylinder, a hollow pipeor tube, a porous polymeric structure, etc. An example of a porousstructure is a filament wound spindle. Because of the low temperatureand pressure used during the photocuring step, the core can be made frommaterials which cannot withstand the prolonged heating used with heatcurable roller coatings such as those derived from wood, cardboard,synthetic plastics, fiber-reinforced composites, foamed resins orelastomers, etc.

The method of applying the photocurable composition to the roller core(cylinder) is not critical, and can also, typically, be a forced-feedmechanism such as the use of a roller transfer to the core, an extrusiontransfer, a curtain coating a knife coating, etc. Also a dip coating orspray coating technique can be used when the photocurable composition isof a relatively low viscosity.

The photocuring means is an actinic radiation source. It can be anultraviolet radiation source that is composed of one or more individualU.V. sources, e.g., a sun lamp, mercury vapor lamp, carbon arc, pulsedxenon arc, etc., several batteries of individual sources, and so forth.Other actinic electromagnetic or ionizing radiation sources can be used,e.g., electron beams, gamma rays, lasers, visible radiation sources,infrared radiation sources, etc., if the coating composition isformulated properly so that satisfactory rates of curing can be attainedtherewith, and if the radiation can be so directed, focused, orcollimated by shielding or the like so as to photocure the coating onthe core but not the feed stream, etc.

The preferred coating substance is a photocurable composition, andparticularly those having elastomeric properties in the photocuredstate.

The crucial ingredients in the preferred photocurable composition are:

1. about 2 to about 98 parts by weight of an ethylenically unsaturatedpolyene (or polyyne) containing two or more reactive unsaturatedcarbon-to-carbon bonds;

2. about 98 to about 2 parts by weight of a polythiol; and

3. about 0.0005 to about 50 parts by weight [based on 100 parts byweight of l and (2)] of a photocuring rate accelerator.

It is understood, however, that when energy sources other than visibleor ultraviolet light are used to initiate the curing reaction,photocuring rate accelerators (i.e., photosensitizers, etc.) generallyare not required in the formulation. That is to say, the actualcomposition of the photocuring rate accelerator, if required, may varywith the type of energy source that is used to initiate the curingreaction.

The reactive carbon-to-carbon bonds of the polyenes are preferablylocated terminally, near terminally, and/or pendant from the main chain.The'polythiols, preferably, contain two or more thiol groups permolecule. The photocurable compositions are liquid (i.e., flowable) overthe temperature range provided during the application to the rotatingcore.

Included in the term liquid, as used herein, are those photocurablecompositions which in the presence of inert solvent, aqueous dispersionor plasticizer have a viscosity ranging from slightly above 0 to 20million centipoises at C. The term liquids includes suspensions, etc.

As used herein polyenes and polyynes refer to simple or complex speciesof alkenes or alkynes having a multiplicity, i.e., at least two,reactive" carbon-to-carbon unsaturated functional groups per averagemolecule. For example, a diene is a polyene that has two reactivecarbon-to-carbon double bonds per average molecule, while a diyne is apolyyne that contains in its structure two reactive carbon-to-carbontriple bonds per average molecule. Combinations of reactivecarbon-to-carbon triple bonds within the same molecule are alsooperable. An example of this is monovinylacetylene, which is apolyeneyne under our definition. For purposes of brevity all theseclasses of compounds will be referred to herein as polyenes.

As used herein the term reactive" unsaturated carbon-tocarbon groupsmeans groups which will react underproper conditions as set forth hereinwith thiol groups to yield the thioether linkage near as contrasted tothe term unreactive" carbon-to-carbon unsaturation which means groupswhen found in aromatic nuclei (cyclic structures exemplified by benzene,pyridine, anthracene, and the like) which do not under the sameconditions react with thiols to give thioether linkages. In the instantinvention products from the reaction of polyenes with polythiols whichcontain two or more thiol groups per average molecule are calledpolythioether polymers or polythioethers.

Methods of preparing various polyenes, with the limitations set forthherein, useful within the scope of this invention are disclosed incopending application Ser. No. 674,773, filed Oct. 12, i967 nowabandoned, and assigned to the same assignee. Some of the usefulpolyenes are prepared in the detailed examples set forth in thefollowing specification. The general fonnulas for several, useful,representative polyenes and polyynes are given in the Figures in Dutch(Holland) application Ser. No. 67/ 10439 which was laid open to publicinspection and copying thereof on Jan. 29, 1969 (said pertinent portionsof said public document being incorporated herein by reference).

One group of polyenes, with the limitations set forth herein, operablein the instant invention is that taught in a copending applicationhaving Ser. No. 617,801, inventors: Kehr and Wszolek, filed Feb. 23,1967, and assigned to the same assignee. This group includes thosehaving a molecular weight in the range of S0 to 20,000, a viscosityranging from 0 to million centipoises at 703 C. of the general formula:[A]-(X),,,, wherein X is a member of the group consisting of moiety freeof l reactive carbon-tocarbon unsaturation and (2) unsaturated groups inconjugation with the reactive ene or yne groups in X. Thus A may containcyclic groupings and minor amounts of heteroatoms such as N,S, P or 0but contains primarily carbon-carbon, carbon-oxygen or silicon-oxygencontaining chain linkages without any reactive carbonto-carbonunsaturation. This group preferably has a weight over 300.

In this first group, the polyenes are simple or complex species ofalkenes or alkynes having a multiplicity of pendant, terminally or nearterminally positioned reactive carbon-tocarbon unsaturated functionalgroups per average molecule. As used herein for determining the positionof the reactive functional carbon-to-carbon unsaturation, the termterminal means that said functional unsaturation is at an end of themain chain in the molecule; whereas by near terminal is meant that thefunctional unsaturation is not more than four carbon atoms away from anend of the main chain in the molecule. The term pendant" means that thereactive carbon-to-carbon unsaturation is located terminally or nearterminally in a branch of the main chain as contrasted to a position ator near the ends of the main chain. For purposes of brevity all of thesepositions will be referred to generally as terminal unsaturation.

The liquid polyenes operable in this first group contain one or more ofthe following types of nonaromatic and nonconjugated reactivecarbon-to-carbon unsaturation:

0 0 II II II and the like, so as to fonn a conjugated system ofunsaturated bonds exemplified by the structure:

On the average the polyenes must contain two or more reactiveunsaturated carbon-to-carbon bonds per molecule and have a viscosity inthe range from slightly above 0 to about 20 million centipoises at 70 C.Included in the term polyenes" as used herein are those materials whichin the presence of an inert solvent, aqueous dispersion or plasticizerfall within the viscosity range set out above at 70 C. Operable polyenesin the instant invention have molecular weights in the range of about 50to about 20,000, preferably about 500 to about 10,000.

Examples of operable polyenes from this first group include, but are notlimited to:

l. Crotyl-terminated polyurethanes which contain two reactive" doublebonds per average molecule in a near terminal position of the averagegeneral formula:

4. The following structure which contains near terminal reactive doublebonds:

wherein x is at least I. 5

A second group of polyenes operable in this invention includes thosepolyenes in which the reactive unsaturated carbon-to-carbon bonds areconjugated with adjacent unsaturated groupings. Examples of operableconjugated reactive ene systems include but are not limited to thefollowing:

0 H P l A few typical examples of polymeric polyenes which containconjugated reactive double-bond groupings such as those described aboveare poly(oxyethylene) glycol (600 M.W.) diacrylate;poly(oxytetramethylene) glycol (L000 M.W.) dimethacrylate; thetriacrylate of the reaction product of trimethylol propane with 20 molesof ethylene oxide; and the like.

As used herein, the term polythiols refers to simple or complex organiccompounds having a multiplicity of pendant or terminally positioned SHfunctional groups per average molecule.

On the average the polythiols must contain two or more SH groups permolecule. They usually have a viscosity range of slightly above to about20 million centipoises (c.p.s.) at 70? C., as measured by a BrookfieldViscometer. Included in the term polythiols" as used herein are thosematerials which in the presence of an inert solvent, aqueous dispersionor plasticizer fall within the viscosity range set out above 70 C.Operable polythiols in the instant invention usually have molecularweights in the range about 50 to about 20,000, or more, preferably about100 to about 10,000.

The polythiols operable in the instant invention can be exemplified bythe general formulas: R,,-(SH),, wherein n is at least 2 and R, is apolyvalent organic moiety free from reactive" carbon-to-carbonunsaturation. Thus R, may contain cyclic groupings and minor amounts ofheteroatoms such as N, S, P or 0 but primarily contains carbon-hydrogen,carbonoxygen, or silicon-oxygen containing chain linkages free of anyreactive" carbon-to-carbon unsaturation.

One class of polythiols operable with polyenes in the instant inventionto obtain essentially odorless compositions are esters ofthiol-containing acids of the general formula: HS- R,CO0H, wherein R, isan organic moiety containing no reactive" carbon'to-carbon unsaturationwith polyhydroxy compounds of the general structure: R (()l-l),, whereinR is an organic moiety containing no reactive carbon-to-carbonunsaturation and n is 2 or greater. These components will react undersuitable conditions to give a polythiol having the general structure:

wherein R and R are organic moieties containing no reactive"carbon-tocarbon unsaturation and n is 2 or more.

Certain polythiols, such as the aliphatic monomeric polythiols (ethanedithiol, hexamethylene dithiol, decamethylene dithiol,tolylene-2,4-dithiol, etc.), some polymeric polythiols, such as athiol-terminated ethylcyclohexyl dimercaptan polymer, etc., and similarpolythiols which are conveniently and ordinarily synthesized on acommercial basis, although having obnoxious odors, are operable in thisinvention. Examples of the polythiol compounds preferred for thisinvention because of their relatively low odor level and fast curingrate include but are not limited to esters of thioglycolic acid(HS-ClhCOOl-l), a-mercaptopropionic acid (HS-CH(CH )COOH) andB-mercaptopropionic acid (HS-ClhCl-hCOOH) with polyhydroxy compoundssuch as glycols, triols, tetraols, pentaols, hexaols, etc. Specificexamples of the preferred polythiols include but are not limited toethylene glycol bis(thioglycolate), ethylene glycolbis(B-mercaptopropionate), trimethylolpropane tris( thioglycolatetrimethylopropane tris( B-mercaptopropionate), pentaerythritoltetrakis(thioglycolate) and pentaerythritoltetrakis(fi-mercaptopropionate), all of which are commerciallyavailable. A specific example of a preferred polymeric polythiol ispoly(propylene ether) glycol bis(B-mercaptopropionate) which is preparedfrom poly(propylene ether) glycol (e.g., Pluracol P 2010, WyndotteChemical Corp.) and B-mercaptopropionic acid by esterification.

The preferred polythiol compounds are characterized by a low level ofmercaptanlike odor initially, and after reaction give essentiallyodorless cured polythioether end products which are commercially usefulresins or elastomers for printing plates.

As used herein the term odorless means the substantial absence of thewell-known offensive and sometimes obnoxious odors that arecharacteristic of hydrogen sulfide and the derivative family ofcompounds known as mercaptans.

The term functionality as used herein refers to the average number ofone or thiol groups per molecule in the polyene and/or the polythiol.For example, a triene is a polyene with an average of three rmtivecarbon-to-carbon unsaturated groups per molecule and thus has afunctionality of 3. A dithiol is a polythiol with an average of twothiol groups per molecule and thus has a functionality of 2.

It is further understood and implied in the above definitions that inthese systems the functionality of the polyene and the polythiolcomponent is commonly expressed in whole numbers although in practicethe actual functionality may be fractional. For example, a polyenecomponent having a nominal functionality of 2 (from theoreticalconsiderations alone) may in fact have an effective functionality ofsomewhat less than 2. Such a product is useful in the instant inventionand is referred to herein as having a functionality of 2.

To obtain the maximum strength, solvent resistance, creep resistance,heat resistance and freedom from tackiness, the reaction componentsconsisting of the polyenes and polythiols of this invention generallyare formulated in such a manner as to give solid, cross-linked, threedimensional network polythioether polymer formation, the individualpolyenes and polythiols must each have a functionality of at least 2 andthe sum of the functionalities of the polyene and polythiol componentsmust always be greater than 4. Blends and mixtures of the polyene andthe polythiols containing said functionality are also operable herein.

The preferred photocurin g reaction can be initiated by UV. radiationcontained in actinic radiation from sunlight or obtained from speciallight sources which emit significant amounts of U.V. light. (Useful UV.radiation generally has a wavelength in the range of about 2,000 toabout 4,000 angstrom units.) Thus it is possible merely to expose thepolyene and polythiol admixture to actinic radiation under ambientconditions or otherwise and obtain a cured solid elastomeric or resinousproduct useful as a core coating material. But this approach to theproblem results in extremely long exposure times which cause the processin the vast bulk of applications to be commercially unfeasible. Chemicalphotocuring rate accelerators (photoinitiators or photosensitizers orphotoactivators) e.g., quinone, methyl ethyl ketone, etc., serve todrastically reduce the exposure time and thereby when used inconjunction with various forms of energetic radiation (containing U.V.radiation) yield very rapid, commercially practical photocures by thepractice of the instant invention. Useful photocuring rate acceleratorsinclude benzophenone; acetophenone; acenapthenequinone; methyl ethylketone; thioxanthen-Q-one; xanthen-Q-one; 7-H-Benz [de] antracen-7- one;dibenzosubemone; l -naphthaldehyde; 4 ,4 bis(dimethylamino)benzophenone; fluorene-9-one; lacetonaphthone; 2'-acetanaphthone;2,3-butanedione; anthraquinone; l-indanone; 2-tert-butyl anthraquinone;valerophenone; hexanophenone; 8-phenylbutyrophenone;prnorpholinopropiophenone; 4-morpholinobenzophenone; 4'-

morpholinodesoxybenzoin; p-diacetylbenzene; 4- aminobenzophenone;4'-methoxyacetophenone; benzaldehyde; a-tetralone; Q-acetyIphenanthrene;2- acetylphenanthrene; IO-thioxanthenone; 3-

acetylphenanthrene; 3-acetylindole; 1,3,5-triacetylbenzene; etc., andblends thereof. The photoinitiators are added in an amount ranging fromabout 0.0005 to about 50 percent by weight of the polyene and polythiolcomponents in the instant invention. Benzophenone is the preferredphotocuring rate accelerator.

The compositions to be photocured, i.e., converted to roller corecoatings, in accord with the present invention may, if desired, includesuch additives as antioxidants, inhibitors, ac-

tivators, fillers, pigments, dyes, antistatic agents, flame-retardantagents, thickeners, thixotropic agents, surface-active agents, viscositymodifiers, plasticizers, and the like within the scope of thisinvention. Such additives generally are preblended with the polyene orpolythiol prior to impregnating it in and/or on the ultimate structure.The aforesaid additives may be present in quantities up to 500 parts ormore per 100 parts photocurable composition by weight and preferably0.0005 to 300 parts on the same basis. The type and concentration of theadditives must be selected with great care so that the final compositionremains photocurable under conditions of exposure.

The compounding of the components prior to photocuring can be carriedout in any conventional manner which takes into account that thematerial is sensitive to UV. radiation. This composition generally canbe stored in the dark for extended periods of time prior to actual useor even incorporation in and/or on the ultimate structure.

It is often desirable to place a suitable antioxidant, e.g., lonol,hydroquinone, t-butyl catechol, etc., in the photocurable composition.These agents in optimum amounts will help to stabilize the fullyformulated composition against premature thickening or curing duringperiods of storage prior to the use in the coating process.

The above discussion about photocurable compositions applies to thephotocurable compositions used in both coating layer and the finishinglayer.

The following examples will aid in explaining, but should not be deemedas limiting, the instant invention. In all cases, unless otherwisenoted, all parts and percentages are by weight.

EXAMPLE 1 3456.3 g. (1.75 mole) of poly(propylene ether) glycol,commercially available under the trade name PPG 2025 from Union Carbide,and 1.7 g. of di-n-butyl tin dilaurate were placed in a 5-liter,round-bottom, three-neck flask. The mixture in the flask was degassed at110I1C. for 1 hour and was then cooled to 25.C. by means of an externalwater bath. Two hundred and seven grams (3.50 moles) of allyl alcohol,with stirring, were added to the flask. 609.0 g. (3.50 moles) of an 80to 20 percent isomer mixture of tolylene-2,4-di-isocyanate andtolylene-2,6-diisocyanate, respectively, sold under the trade nameMondur TD 80, was charged to the flask. The mixture was stirred well.The flask was cooled by the water bath during this period. Eight minutesafter the Mondur TD 80" was added, the temperature of the mixture was59' C. After 20 minutes, the NCO content was 12.39 mg. NCO/g; after 45minutes, it was 9.87 mg. NCO/g; and after 75 minutes, it was 6.72 mg.NCO/g. The water bath was removed 80 minutes after the Mondur TD 80 hadbeen added, the temperature of the mixture being 41 C., and heat wasapplied until the mixture temperature reached 60 C. That temperature wasmaintained. One hundred and five minutes after the Mondur TD 80" wasadded, the NCO content was 3.58 mg. NCO/g; after 135 minutes, it was1.13 mg. NCO/g; and after 195 minutes, it was 0.42 mg. NCO/g. At thatpoint in time, the resultant polymer composition was heated to 70 C.,and vacuum-stripped for 1 hour. The resultant polymer composition waslabeled composition 1, and had a viscosity of 16,000 c.p.s. as measuredon a Brookfield Viscometer at 30 C. Unless otherwise stated, all theviscosity measurements were made on a Brookfield Viscometer at 30C.

The above procedure was repeated five times, and resultant compositionswere labeled compositions 2 to 6, respectively. The heating step lasted180 minutes, 140 minutes, 205 minutes and 180 minutes, respectively.With composition 2, the temperature was 60 C. after 8 minutes; withcomposition 3, the temperature was 57 C. after 6 minutes; withcomposition 4, the temperature was 41 C. after 20 minutes, at which timethe temperature was raised and held at 60 C.; with composition 5, thetemperature was 57.5 C. in 8 minutes, was 42 C. in 40 minutes, thentaken up to 60 C. and lowered to 58 C. after minutes; and withcomposition 6, the temperature was 57 C. in 6 minutes, and was 41 C.after 60 minutes, at which time the temperature was immediately raisedto 60 C. The viscosity of the resultant polymer compositions was 15,500c.p.s.; 16,000 c.p.s.; 17,000 c.p.s.; 16,800 c.p.s.; and 16,200 c.p.s.respectively.

Compositions l, 2, 3, 4, 5 and 6 were placed in a 6-gallon container andstirred well. The resultant polymer composition had a viscosity of16,000 c.p.s. and the NCO content was 0.01 mg. NCO/g. This compositepolymer composition was labeled polyene A.

EXAMPLE 2 One hundred parts of polyene A, 10 parts of polythiol A, 1.5parts of benzophenone and 0.1 part by weight of lonol" were thoroughlyadmixed. This resulted in photocurable composition A. Polythiol A waspentaerythritol tetrakis-(mercaptopropionate), which is commerciallyavailable under the trade name Q43 Ester (sold by Carlisle ChemicalCompany). lonol is a label designation for 2,6-di-tertbutyl-4-methylphenol (sterically hindered) and is commercially available fromShell Chemical Company. lonol has good antioxidant properties, isnonirritating to the skin, and has a comparatively inert, nonacidichydroxyl group.

Photocurable composition A was placed in a reservoir like the one shownin FIG. 1. The rest of the experiment was similar to that shown in FIG.1 and 2 and the accompanying writeup above. The end of the delivery traywas placed about 20 mils away from the 1.0-inch diameter roll core(steel). The roller core was rotated at 10 r.p.m. The valve on thethroat of the reservoir was opened. As the coating was applied to theroller core, the delivery tray was slowly moved (manually) away from thecore. When the coating thickness reached about one-half inch, thedelivery tray was completely backed away from the coated roller. Thecoated roller was further rotated for 3 minutes before a shutter wasplaced in front of the UV. lamp to turn it off in effect. A coatedroller was produced at this point.

The doctor blade portion of the delivery tray was put in nearly touchingposition with the photocured layer of the rotating coated roller. Abatch of photocurable composition was placed at the end of the deliverytray, which formed a rolling bank. (See FIG. 3) An equal volume amountof toluene was placed on top of the photocurable composition. The coatedroller was rotated a few times to mix the solvent and photocurablecomposition. As the diluted coating was applied to the coated roller,the delivery tray was slowly moved (manually) away from the coatedroller. After a 20-mil additional retractor the delivery tray wascompletely backed away from the coated roller. The roller was furtherrotated for 1 minute to allow partial evaporation of the solvent. Theshutter or shield in front of the UV. lamp was removed and the finishinglayer was photocured for 3 minutes. The resultant coated roller had asmooth glazelike essentially faultless finish. The final hardness of thecoating was measured at Shore A 50 (ASTM).

EXAMPLES 3 to 9 Example 2 was repeated seven times, except that thetoluene was replaced with isopropanol (1:1) (example 3), ethanol (2:1)(example 4), methyl ethyl ketone (1:1) (example 5), methylene chloride(1:3) (example 6), benzene (2:1) (example 7), acetone (1:1) (example 8)and butyl cellosolve (1:1) (example 9), respectively. The above ratiosare expressed on a weight basis of the solvent to photocurablecomposition. The resultant photocured coating had a smooth, uniform,glazelike finish.

EXAMPLE 10 Example 2 was repeated, except that the finish layer wasphotocured immediately after that solvent diluted layer was applied. Theresultant photocured finish was not quite as good as the one obtained inexample 2.

EXAMPLE 1 1 Example 2 was repeated except that 15 parts of polythiol Awas used. The resultant photocured coating had a smooth, uniform,glazelike finish.

EXAMPLES 12 to 15 EXAMPLE 16 Example 2 was repeated, except that half ofthe pen taaerythritol tetrakis(B-mercaptopropionate) was replaced withparts of ethylene glycol bis(B-mercaptopropionate). The resultantphotocured coating had a smooth, uniform, glazelike finish.

EXAMPLE 17 Example 2 was repeated except that 60 parts of polyene B wasused in place of polyene A. Polyene B was prepared as follows: 458 g.(0.23 mole) of a commercially available liquid polymeric diisocyanatesold under the trade name Adiprene Ll00"by E. l. duPont de Nemours & Co.was charged to a dry resin kettle maintained under a nitrogen atmosphereand equipped with a condenser, stirrer, thermometer, and gas inlet andoutlet. 37.8 g. (0.65 mole) of allyl alcohol was charged to the kettleand the reaction was continued for 17 hours with stirring at 100 C.Thereafter the nitrogen atmosphere was removed and the kettle wasevacuated 8 hours at 100 C. 50 cc. dry benzene was added to the kettleand the reaction product was azeotroped with benzene to remove theunreacted alcohol. This allyl-terminated liquid polymer had a molecularweight of approximately 2,100 and was labeled polyene B.

The resultant photocured coating had a smooth, uniform, glazelikefinish.

EXAMPLE 18 Example 2 was repeated except that lOO parts of polyene C wasused in place of polyene A. Polyene D was prepared as follows: 1,500 g.(0.47 mole) of a linear solid polyester diol having a molecular weightof 3,200 and commercially available from Hooker Chemical Corp. under thetrade name Rucoflex S-lOl 1-35 was charged to a 3-liter, three-neckedflask and heated to 110 C. under vacuum and nitrogen for 1 hour withstirring. Eighty-three grams of allyl isocyanate having a molecularweight of 83.1 and commercially available from Upjohn Co. was added tothe flask along with 0.3 cc. of dibutyl tin dilaurate (catalyst),commercially available from J. T. Baker Co. The reaction was continuedat 1 C. with stirring for 1 hour. This allyl-terminated polymer waslabeled polyene C.

The resultant photocured coating had a smooth, uniform glazelike finish.

EXAMPLE 19 to 24 Example 2 was repeated six times, except that thebenzophenone was replaced with cyclohexanone (2.0 parts) (lpart)(example 24), respectively. The resultant photocured coatings hadsmooth, uniform, glazelike finishes.

EXAMPLES 25 and 26 Example 2 was repeated twice, except that the rolledcore was constructed of copper and fiber glass reinforced polyesterresin, respectively. The resultant photocured coatings had smooth,uniform, glazelike finishes.

EXAMPLE 27 This example illustrates the use of a monomeric polythiol anda monomeric polyene. 23.8 g. of pentaerythritoltetrakis(B-mercaptopropionate); 25.6 g. of the reaction product of 1mole of 1,4-butanediol with 2 moles of allyl isocyanate; and 0.5 g. ofbenzophenone were thoroughly admixed. Example l was repeated, exceptthat the above I photocurable composition was used in place ofphotocurable composition A. The resultant photocured coating had asmooth, uniform, glazelike finish.

EXAMPLE 28 This example illustrates the use of a reactive ene groupconjugated with another double-bond grouping (C 0). Twentyseven grams ofthe triacrylate of the reaction product of 1 mole of trimethylol propanewith 20 moles of ethylene oxide; 9 g. of pentaerythritoltetrakis(B-mercaptopropionate); and 0.5 g. of benzophenone werethoroughly admixed. Example 1 was repeated, except that the abovephotocurable composition was used in place of photocurable compositionA. The resultant photocured coating had a smooth, uniform, glazelikefinish.

EXAMPLE 29 Example 1 was repeated, except that the photocuringcomposition used in diluted form to prepare the finishing layer was thephotocurable composition used in example 28. The resultant photocuredcoating had a smooth, uniform, glazelike finish.

EXAMPLE 30 This example illustrates the use of a photocurablecomposition containing a monomeric polyene and a polymeric polythiol.Fifty grams of Dion Polymercaptan Resin DPM-1002 which is a thiolterminated liquid polymer having a functionality of 2 to 3 and amolecular weight of about 5,000 and commercially available from DiamondAlkali Company; 2.5 g. of triallyl cyanurate; and 0.5 g. of benzophenonewere admixed. Example 2 was repeated, except that the above photocurablecomposition was used in place of photocurable composition A. Theresultant photocured coating had a smooth, uniform, glazelike finish.

EXAMPLE 31 This example illustrates the use of a photocurablecomposition containing a polymeric polyene and a polymeric polythiol.Example 2 was repeated, except that the photocurable compositioncontained 50 parts of the polymeric polyene used in example 16; parts ofthe polymeric polythiol used in example 27; and 0.5 part ofbenzophenone. The resultant photocured coating had a smooth, uniform,glazelike finish.

EXAMPLE 32 Example 2 was repeated, except that as the toluene-dilutedphotocurable material was coated, more toluene was added until nearlypure toluene'was being coated. The resultant photocured coating had asmooth, uniform, glazelike finish.

EXAMPLE 33 Example 2 was repeated, except that the toluene-dilutedphotocurable material was admixed, placed in a reservoir and coated inthe same manner the undiluted photocurable composition. The resultantphotocured coating had a smooth, glazelike finish.

EXAMPLE 34 Example 2 was repeated, except that the photocurablecomposition contained phthalocyanine blue as a pigment. The resultantphotocured coating had a smooth, glazelike finish.

EXAMPLE 35 Example 2 was repeated up to the point where there was only asmall amount of photocurable composition A was left to be coated. Thesolvent used in example 2 was then slowly added to the rolling bank ofphotocurable composition A. The solvent-diluted composition was thenfurther coated as in example 2. The resultant photocured coating had asmooth, uniform, glazelike finish.

What is claimed is:

l. A process for preparing a coated cylindrical core, said coatinghaving a smooth glazelike finish, which comprises:

a. coating a first photocurable composition on a rotating cylindricalcore;

b. photocuring said photocurable composition coating on said rotatingcylindrical core to form a photocured layer whereby said photocuring isachieved by subjecting said photocurable composition to actinicradiation;

c. coating a second photocurable composition which is diluted relativeto said first composition with a solvent on said photocured layer onsaid rotating cylindrical core; and

d. photocuring said solvent-diluted photocurable composition, wherebysaid photocuring is achieved by subjecting said photocurable compositionto actinic radiation and whereby a smooth glazelike finish layer isformed on said photocured coating layer, said layers being essentiallyone monolithic layer and said solvent having substantially evaporatedfrom said finish layer.

2. A process as described in claim 1 wherein said photocuring isachieved by means of ultraviolet radiation 3. A process as described inclaim 1 wherein said photocuring is achieved by means of electron beamradiation.

4. A process as described in claim 1 wherein said solvent is toluene.

5. A process as described in claim 1 wherein said coated rollercontaining said photocurable finishing layer is rotated for a period oftime between steps (c) and (d), whereby a substantial portion of saidsolvent evaporates before step (d) is conducted.

6. A process as described in claim 1 wherein said coating step (a) andsaid photocuring step (b) occur simultaneously, said photocuringoccurring in the freshly coated layer and in several previously coatedlayers.

7. A process as described in claim 1 wherein said photocurablecomposition used in step (a) and step (c) comprises an ethylenicallyunsaturated polyene having at least two reactive ene groups permolecule, a polythiol containing two or more thiol groups per molecule,and a photocuring rate accelerator, where the sum of the functionalitiesof said polyene and said polythiol is greater than 4.

8. A process as described in claim 7 wherein the photocura' blecomposition in said photocurable layer is comprised of 2 to 98 parts byweight of said polyene, 98 to 2 parts by weight of said polythiol, and0.0005 to 50 parts by weight photocuring rate accelerator based on 100parts by weight of said polyene and said polythiol.

9, A process as described in claim 8 wherein said polyene compositionhas a molecular weight in the range of 50 to 20,000; has a viscosityranging from essentially 0 to 20 million centipoises at C.; and has ageneral formula: [A]-(X),,, wherein X is a member of the groupconsisting of and R-C C-; m is an integer of at least 2; R isindependently selected from the group consisting of hydrogen, halogen,and an organic compound selected from the group consisting of aryl,substituted aryl, aralkyl, substituted aralkyl, cycloalkyl, substitutedcycloalkyl, alkyl and substituted alkyl groups containing one to fourcarbon atoms; and A is a polyvalent polymeric organic moiety free of l)reactive carbon-to-carbon unsaturation, and (2) unsaturated groupings interminal conjugation with X.

10. A process as described in claim 8 wherein the polyene has amolecular weight in excess of 300.

11. A process as described in claim 8 wherein the photocurablecomposition contains 0.0005 to 5.0 parts by weight of an antioxidant,0.05 to 25 parts by weight of a pigment, 1.0 to 50 parts by weight of aplasticizer, and 0.5 to 100 parts by weight of a filler, each of saidingredients being based upon 100 parts by weight of said polyene andsaid polythiol.

12. A process as described in Claim 1 1 wherein said antioxidant is2,6-di-tert-butyl4-methylphenol.

13. A process as described in claim 8 wherein the two or more reactiveene groups are located terminally in the molecule or where the two ormore reactive ene groups are conjugated with other unsaturated groups.

14. A process as described in claim 8 wherein the said polythiol has amolecular weight between about 50 and about 20,000, and has a viscositybetween slightly above 0 and about 20 million centipoises at 70 C.

15. A process as described in claim 8 wherein said polyene is preparedfrom allyl alcohol, polyalkylene ether glycol and tolylene diisocyanate.

16. A process as described in claim 7 wherein the same photocurablecomposition is used in step (a) and step (c).

17. A process as described in claim 7 wherein difierent photocurablecompositions are used in step (a) and step (c).

18. An article of manufacture which comprises (i) a cylindrical core,(ii) a photocured coating layer and (iii) a photocured smooth, glazelikefinishing layer, said layer (ii) and said layer (iii) being essentiallyone monolithic layer. 3

2. A process as described in claim 1 wherein said photocuring isachieved by means of ultraviolet radiation
 3. A process as described inclaim 1 wherein said photocuring is achieved by means of electron beamradiation.
 4. A process as described in claim 1 wherein said solvent istoluene.
 5. A process as described in claim 1 wherein said coated rollercontaining said photocurable finishing layer is rotated for a period oftime between steps (c) and (d), whereby a substantial portion of saidsolvent evaporates before step (d) is conducted.
 6. A process asdescribed in claim 1 wherein said coating step (a) and said photocuringstep (b) occur simultaneously, said photocuring occurring in the freshlycoated layer and in several previously coated layers.
 7. A process asdescribed in claim 1 wherein said photocurable composition used in step(a) and step (c) comprises an ethylenically unsaturated polyene havingat least two reaCtive ene groups per molecule, a polythiol containingtwo or more thiol groups per molecule, and a photocuring rateaccelerator, where the sum of the functionalities of said polyene andsaid polythiol is greater than
 4. 8. A process as described in claim 7wherein the photocurable composition in said photocurable layer iscomprised of 2 to 98 parts by weight of said polyene, 98 to 2 parts byweight of said polythiol, and 0.0005 to 50 parts by weight photocuringrate accelerator based on 100 parts by weight of said polyene and saidpolythiol. 9, A process as described in claim 8 wherein said polyenecomposition has a molecular weight in the range of 50 to 20,000; has aviscosity ranging from essentially 0 to 20 million centipoises at 130*C.; and has a general formula: (A)-(X)m wherein X is a member of thegroup consisting of and R-C C-; m is an integer of at least 2; R isindependently selected from the group consisting of hydrogen, halogen,and an organic compound selected from the group consisting of aryl,substituted aryl, aralkyl, substituted aralkyl, cycloalkyl, substitutedcycloalkyl, alkyl and substituted alkyl groups containing one to fourcarbon atoms; and A is a polyvalent polymeric organic moiety free of (1)reactive carbon-to-carbon unsaturation, and (2) unsaturated groupings interminal conjugation with X.
 10. A process as described in claim 8wherein the polyene has a molecular weight in excess of
 300. 11. Aprocess as described in claim 8 wherein the photocurable compositioncontains 0.0005 to 5.0 parts by weight of an antioxidant, 0.05 to 25parts by weight of a pigment, 1.0 to 50 parts by weight of aplasticizer, and 0.5 to 100 parts by weight of a filler, each of saidingredients being based upon 100 parts by weight of said polyene andsaid polythiol.
 12. A process as described in Claim 11 wherein saidantioxidant is 2,6-di-tert-butyl-4-methylphenol.
 13. A process asdescribed in claim 8 wherein the two or more reactive ene groups arelocated terminally in the molecule or where the two or more reactive enegroups are conjugated with other unsaturated groups.
 14. A process asdescribed in claim 8 wherein the said polythiol has a molecular weightbetween about 50 and about 20,000, and has a viscosity between slightlyabove 0 and about 20 million centipoises at 70* C.
 15. A process asdescribed in claim 8 wherein said polyene is prepared from allylalcohol, polyalkylene ether glycol and tolylene diisocyanate.
 16. Aprocess as described in claim 7 wherein the same photocurablecomposition is used in step (a) and step (c).
 17. A process as describedin claim 7 wherein different photocurable compositions are used in step(a) and step (c).
 18. An article of manufacture which comprises (i) acylindrical core, (ii) a photocured coating layer and (iii) a photocuredsmooth, glazelike finishing layer, said layer (ii) and said layer (iii)being essentially one monolithic layer.